Calculate how many gallons or liters of paint you need. Accounts for doors, windows, and number of coats.
Step 1: Calculate total wall area. For a rectangular room: Wall area = 2 x (Length + Width) x Height
Step 2: Subtract openings. Standard door = ~21 sq ft (3 x 7 ft). Standard window = ~15 sq ft (3 x 5 ft).
Step 3: Multiply by number of coats. Most interior paint jobs require 2 coats for proper coverage.
Step 4: Divide by paint coverage rate. Standard interior latex paint covers approximately 350 sq ft per gallon.
Formula: Gallons = (Wall area - openings) x coats / coverage per gallon
Interior latex paint: 350-400 sq ft per gallon on smooth surfaces.
Exterior paint: 250-350 sq ft per gallon depending on surface texture.
Primer: 200-300 sq ft per gallon. Always prime new drywall and when making drastic color changes.
Textured walls: Reduce coverage by 15-25% for rough or textured surfaces.